Those stimulus factors which promote the externalization of sound when presented through earphones will be investigated. This will involve primarily the study of binaural temporal differences of sounds originally recorded in anechoic and echoic environments and their spectral composition. The extent of perceived externalization will be quantified and a statistical analysis of the data will be performed. In addition, the spectral basis for monaural localization in the horizontal plane will be examined. The experimental design will be based on the supposition that monaural localization of sound is an expression of the tonotopic organization of the auditory nervous system. Accordinly, spatial referents of narrow bands of noise differing in center frequency will be investigated and the role of these restricted frequency regions in the locatization of broadband noise will be assessed. BIBLIOGRAPHIC REFERENCES: Belendiuk, K. and Butler, R.A. Monaural localization of low-pass noise bands in the horizontal plane. J. Acoust. Soc. Am., 1975, 58, 701-705. Butler, R.A. and Planert N. The influence of stimulus bandwidth on localization of sound in space. Perception and Psychophysics, 1976, 19, 103-108.